大学英语：Some states have an income tax similar to that of the federal government

　　句中的that用来代替the加前述名词tax，以免重复。

　　请翻译下面的句子：

　　1) 南京的天气比青岛的天气热。（The weather of Nanjing is hotter than that of Qingdao.）

　　2) 黄金的价格比白银的价格要高。（The price of gold is higher than that of silver.）

　　8. Other states have a sales tax, which is a percentage charged to any item which you buy in that state.

　　句中前一个which 引导的是一个非限定性定语从句，修饰sales tax。非限定性定语从句通常在句中起进一步说明作用，既可修饰先行词也可修饰整个句子。如果省去，原句意义不受影响。非限定性定语从句有逗号。